Hybrid electric vehicles (HEVs) have a powertrain that includes a propulsion engine, such as a combustion engine (CE) and an electric machine/generator or electric motor generator/starter (EM), which generate power and torque to propel the vehicle. Unlike a conventional driveline with an automatic transmission where a fluid coupling torque converter is present, HEVs may have a power split powertrain transfer the torques from the CE and EM to the vehicle driveline and wheels with less mechanical damping. Controlling such HEVs to ensure favorable occupant drivability perceptions, requires reduction of undamped or insufficiently damped noise and vibration, especially when transiting between from electric and CE modes that require a stopped CE to restart.
Power split HEV powertrains include a planetary gear set having speed ratios that enable control of engine and/or CE speed, by controlled EM speed torque signals. During a startup cranking phase of CE in such a power split HEV, the EM speed is accelerated to bring the CE speed up to a desired CE speed before the combustion is initiated. During engine and/or CE spool up, the CE and powertrain progresses through one or more possible resonance speed ranges, according to mechanical damping characteristics of the CE, EM, and powertrain, which may include an electronic continuously variable transmission (eCVT). In some circumstances, such possible resonance may be perceptible to vehicle occupants during low HEV speeds when road and other nominal vibrations and noise may otherwise mask CE startup resonances. Previously, such possible resonance(s) were addressed by either reducing the CE spool up time, or by a computationally intensive real-time, thermodynamically-based CE torque control capability.